Universalization of the Phase Diagram for a Model Rod−Coil Diblock Copolymer

The Flory−Huggins interaction is measured for a model rod−coil block copolymer system, poly(alkoxyphenylenevinylene- b -isoprene), by fitting the interfacial segregation of block copolymer to a homopolymer interface and by using the random phase approximation (RPA) for block copolymers. The measured interfacial segregation of a block copolymer to the interface between homopolymers, fit with a self-consistent field theory (SCFT) simulation using χ as a variable parameter, gives a functional form χ = 34.8/ T − 0.091. When RPA is applied to neutron scattering curves for the rod−coil system above the order−disorder transition, the theoretical structure factors are inconsistent with observed scattering curves due to complex aggregated structures formed in the nematic and isotropic states. Using the Flory−Huggins parameter and a previously measured value of the Maier−Saupe parameter, the PPV- b -PI phase diagram may be converted from system-specific variables to dimensionless parameters. Under the assumptions that the rods are ideal nematogens, interaction strengths are composition-independent, and rod−coil and rod−rod interactions are local, this yields the first quantitative universal phase diagram for rod−coil block copolymers.